Local area network for distributing data communication, sensing and control signals

ABSTRACT

A network for carrying out control, sensing and data communications, comprising a plurality of nodes. Each node may be connected to a payload, which comprises sensors, actuators and DTE&#39;s. The network is formed using a plurality of independent communication links, each based on electrically-conducting communication media comprising at least two conductors and interconnecting two nodes, in a point-to-point configuration. During network operation, nodes can be dynamically configured as either data-generating nodes, wherein data is generated and transmitted into the network, or as receiver/repeater/router nodes, wherein received data is repeated from a receiver port to all output ports. During normal network operation, the network shifts from state to state. Each state is characterized by assigning a single node as the data-generating node, and configuring all other nodes in the network as repeaters and receivers. The network can be configured in linear or circular topology, or any mixture of both. The nodes and the payloads can each be powered by local power supply or via the network wiring. In the latter case, dedicated wires can be used, or the same conductors may be employed for both power distribution and communication. Network control can be performed external to the network, or by using the network itself as transport for control messages. Shifting from state to state can be done by selecting sequential nodes to be the data-generating node, or by selecting arbitrary nodes to be the data-generating node.

This is a division of parent co-pending application Ser. No. 11/190,884,filed Jul. 28, 2005, itself a continuation of grandparent applicationSer. No. 09/349,020, filed Jul. 7, 1999, now U.S. Pat. No. 6,956,826,issued Oct. 18, 2005.

FIELD OF THE INVENTION

The present invention relates to the field of wired communication andcontrol networks, and, more particularly, to local area networks andnetworks used for sensing, communication, and control.

BACKGROUND OF THE INVENTION

Local area networks (LANs) for distributing data communication, sensing,and control signals are often based on a “bus” topology, as shown inFIG. 1. Such a network 10 relies on shared electrically-conductingcommunication media 1, usually constituted by a twisted-pair ofelectrical conductors or a coaxial cable. Network data terminalequipment (DTE) units 5, 6, and 7 are connected via respective networkadapters 2, 3, and 4 to communication media 1. Network adapters 2, 3,and 4 function as data communication equipment (DCE) units, and aretapped into communication media 1, forming parallel electricconnections, and-thereby interface between DTE units 5, 6, and 7 andcommunication media 1. Such network adapters are also commonly referredto as “NIC”, an example of which is the Network Interface Card IEEE 802(Ethernet). Such a topology is commonly used for connecting personalcomputers (PCs) in a network. Network adapters can be stand-alone units,integrated into the DTE unit or housed therewith in a common enclosure.

Control networks, interconnecting sensors, actuators, and DTE's alsocommonly use the same topology, such as the network described in U.S.Pat. No. 4,918,690 (Markkula, Jr. et al.) and shown in FIG. 2. In anetwork 20, network adapters 22, 23, and 24 function as DCE's, but arecommonly referred to as “nodes”. The payloads 25, 26, and 27 arecomposed of sensors, actuators, and DTE's.

Hereinafter, the term “node” is used for both control anddata-communication applications.

A topology (such as bus topology) whose physical layer communicationmedia employs multi-point connections, is not optimal for communication,and exhibits the following drawbacks:

-   -   1. The maximum length of the communication media is limited.    -   2. The maximum number of units connected to the bus is limited.    -   3. Complex transceivers are required in order to interface the        communication media.    -   4. The data rate is limited.    -   5. Terminators are required at the communication media ends,        thus complicating the installation.    -   6. At any given time, only single connected unit may transmit;        all others are receiving.    -   7. In case of short circuit in the bus, the whole network fails.        Localizing the fault is very difficult.

Despite these drawbacks, however, bus topology offers two uniqueadvantages:

-   -   1. If the application requires “broadcast” data distribution,        where the data generated by a given node must be distributed to        all (or a majority of) the nodes in the network, network        operation is very efficient. This is because only a single        network operation is required (i.e., to establish which node is        the transmitter). The broadcast data is received by all other        nodes in the network in parallel without additional network        overhead.    -   2. The broadcast message is received simultaneously by all        receiving nodes in the network. This is important in real-time        control applications, for example, where orderly operation of        the units must be maintained.

The communication-related drawbacks described above are solved bynetworks constructed of multiple communication links, wherein eachinstance of the link communication media connects only two units in thenetwork. Here, the physical layer in each segment is independent ofother links, and employs a point-to-point connection. Data and/ormessages are handled and routed using data-link layer control. Oneexample of such system for LAN purposes is the Token-Ring, described inthe IEEE 802 standard. An example of a corresponding control network isdescribed in U.S. Pat. No. 5,095,417 to Hagiwara et al. Both networksuse circular topology (“ring topology”) as illustrated in FIG. 3. Anetwork 30 interconnects nodes (or NIC's) 32, 33, and 34 by threeseparate cables 31A, 31B, and 31C, each connecting a pair of nodes andforming three distinct physical layer communication links. Payloads (orDTE's) 35, 36, and 37 are respectively connected to the appropriatenodes.

Both the Hagiwara network and the Token-Ring network use unidirectionalcommunication in each communication link and require a circulartopology. The PSIC network described in U.S. Pat. No. 5,841,360 to thepresent inventor teaches a similar network where the use of a circulartopology is optional, and bi-directional communication (eitherhalf-duplex or full-duplex mode) is employed in the communication links.

The above-mentioned prior art patents -and networks are representativeonly. Certain applications are covered by more than one issued patent.Additional discussion concerning the above-mentioned topologies can befound in U.S. Pat. No. 5,841,360 entitled. “Distributed serial controlsystem” which issued Nov. 24, 1998 and co-pending U.S. patentapplication Ser. No. 09/123,486 filed Jul. 28, 1998, both in the name ofthe present inventor, and incorporated by reference for all purposes asif fully set forth herein.

Networks such as those illustrated in FIG. 3 typically use a “store andforward” mechanism, wherein the data received at a specific node isdecoded at least to the data-link layer, and then re-encoded andtransmitted to another point in the network as determined by the networkcontrol. This use of point-to-point communication links eliminates thecommunication drawbacks enumerated above in broadcast-based networks,but it lacks the two unique advantages of the broadcast technology, asalso previously enumerated. Because the data is not inherentlydistributed throughout a network based solely on point-to-pointcommunication links, such a network incurs a heavy overhead whenbroadcast is needed and exhibits delays in the propagation of messages.The overhead and delays result from the need to decode and re-encodemessages at each node.

There is thus a widely-recognized need for, and it would be highlyadvantageous to have, a means of implementing a network which allows forboth improved communication characteristics, while also supportingbroadcast discipline and fast message distribution along the network.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a local area networkin which at least some of the drawbacks described above are reduced oreliminated.

To this end, the present invention provides a local area network basedon nodes connected to payloads. The nodes are interconnected to form anetwork of half-duplex or full-duplex communication links based onelectrically conducting communication media such as twisted conductorpairs or coaxial cables. Each communication link interconnects two nodesin the network. Each node is capable of being dynamically configured asa transmitter or as a receiver. In addition, however, each receivingnode can also be dynamically configured to be a repeater, which simplyretransmits the received data. In this way, data from one link can berepeated to all other links via an automatic multicast process. Innormal operation, a specific node is selected as the data generatingunit to transmit data to the network. All other nodes serve as repeatersand receivers, and hence the data is multicast instantaneously from theselected data generating node throughout the network. After completingthis transmitting session, another node may be selected as the datagenerating node, with all other nodes serving as repeaters and receiversin a like fashion.

A network according to the present invention can also be configured in acircular topology, enabling operation to continue even when there is amalfunction or loss of a communication link.

Therefore, according to the present invention there is provided a localarea network for distributing data communication, sensing, and controlsignals, the local area network including at least three nodes having anoperational mode and interconnected by at least two distinctcommunication links according to a topology, wherein: (a) each of thecommunication links has at least two electrical conductors; (b) each ofthe communication links connects two of the nodes in a point-to-pointconfiguration; (c) each of the communication links is operative tocommunicating in a half-duplex mode; (d) at least one of the nodes isconnected to a payload; (e) at least two of the nodes have theoperational mode selectable as a data-generating operational mode; (f)at least one of the nodes has the operational mode selectable as arepeating operational mode; and wherein the local area network has astate selectable from a group of at least two distinct states, whereineach state is characterized by having a single selected one of the nodesin the data-generating operational mode, with the remainder of the nodesin operational modes selected from a group containing the receivingoperational mode and the repeating operational mode.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, some preferred embodiments will now he described, byway of non-limiting example only, with reference to the accompanyingdrawings, in which:

FIG. 1 shows a prior-art LAN for data communication, employing bustopology.

FIG. 2 shows a prior-art LAN for control, employing bus topology.

FIG. 3 shows a prior-art network for control or data-communication,employing circular topology.

FIG. 4 describes a general block diagram of a node according to thepresent invention.

FIGS. 5 a, 5 b, 5 c, and 5 d show different possible states of a nodeaccording to the present invention.

FIG. 6 shows a state of a network according to the present invention.

FIG. 7 shows a general block diagram of a node according to theinvention, wherein power is also carried by the network.

FIG. 8 shows a state of a network according to the present invention,wherein power is carried by the network and employing circular topology.

FIGS. 9 a and 9 b show different possible states of a node in circulartopology network according to the present invention.

FIG. 10 shows a block diagram of a node according to a preferredembodiment.

FIG. 11 shows a block diagram of a node according to the presentinvention, supporting three line couplers.

FIG. 12 describes various possible node states, and the respectiverequired switches states for a node as shown in FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principles and operation of a network according to the presentinvention may be understood with reference to the drawings and theaccompanying description. The drawings and descriptions herein areconceptual only. In actual practice, a single circuit can implement oneor more functions; alternatively, each function can be implemented by aplurality of components and circuits. In the drawings and descriptions,identical reference numerals indicate those components that are commonto different embodiments or configurations.

FIG. 4 schematically shows a node 40 according to the present invention.Node 40 contains the following functional blocks:

-   -   A power supply 41, fed from a power source 52, which converts        incoming power to the voltage, or voltages, required by the node        and the node's components. In addition, power supply 41 may also        feed a payload 49 connected to node 40. If used, this feeding        function is carried out by a payload interface 48. (For clarity,        FIG. 4 omits the individual connections distributing power from        power supply 41 to the power-consuming blocks of node 40.)    -   A payload interface 48 which adapts node 40 to a specific        payload 49. Various payload types can be employed, such as        sensors, actuators and data units, either analog or digital,        functioning either as output or as input. For example:        -   Analog sensor. The payload consists of analog sensor used to            measure any physical phenomena. In most cases, the payload            interface contains an A/D converter.        -   Digital sensor. The payload is a switch, button etc.        -   Analog actuator. In most cases the payload contains a D/A            converter controlling the parameters of the analog actuator.        -   Data related unit. In the case of digital communication, the            payload consists of DTE and the payload interface contains a            DTE interface.        -   Non-digital data. Data such :as video, voice, analog            communication or any other of data type. If analog data is            input to the node, the payload interface is likely to-use an            A/D converter. The above examples are not intended to limit            in any way the general payload definition. Furthermore,            multiple devices of various types can be used. In some            cases, payload 49 may use power from node 40. For example,            the excitation voltage to analog sensor may be driven from            the node power. Some nodes in the network may not be            connected to a payload, or may not have any payload            interface at all. Nodes configured in this manner would be            used as repeaters only, such as a node 90 in FIG. 8 Repeater            nodes can be used, for example, to extend the distance            between nodes beyond the regular limit.    -   Line couplers 42 and 43, which interconnect node 40 with up to        two other nodes, each via communication media 50 and 51,        respectively (also referred to as “lines”). Each communication        media supports communication between two nodes of the network.        For clarity only, the two ports are designated ‘Left’-LT and        ‘Right’-RT. The right connection RT uses line 51 and connects        via RT line coupler 43. Similarly, the left connection LT uses        line 50 and connects via LT line coupler 42. Neither line        coupler 42 nor line coupler 43 affects the communication signal.        Line couplers may include connectors, protection devices,        isolation (e.g. transformer) and other required functions, which        are not normally associated with the communication signal        itself.    -   A transmitter 45, which deals with the data to be transmitted,        except for the physical layer functions (according to the OSI        interconnection model). This block can be implemented in        hardware (CRC generation circuitry, for example) by software, or        by both hardware and software.    -   A receiver 46, which deals with the received data except for the        physical layer functions (according to the OSI interconnection        model). This block can be implemented in hardware (CRC error        detection circuitry, for example), by software, or by both        hardware and software.    -   A control, logic, and processing unit 47, which controls and        monitors node 40 and network operation. This block interconnects        with the controlled blocks in node 40 (for clarity, some lines        are omitted from FIG. 4) In addition, control, logic, and        processing unit 47 can process data in the network, and also        deals with the payload via payload interface 48. Control, logic,        and processing unit 47 is furthermore in charge of shifting a        repeater/router 44 from one state to another, as detailed below.    -   Repeater/router 44 deals with the physical layer characteristics        of the communication signal. The repeater/router can be in        various states, including a receive-only state and a        transmit-only state. The signal is encoded and decoded, and is        routed according to the control signals from control, logic, and        processing unit 47. Detailed explanation of the repeater/router        44 follows.

A node can be stand-alone or integrated into the payload. For example,in the case of personal computer, the node can be housed within thecomputer enclosure as an add-on card.

FIGS. 5 a and 5 b describe the various repeater/router functions bymeans of the possible states of a repeater/router during normaloperation. As shown in FIG. 5 a, repeater/router 44 contains two unitsconnected in series. A line receiver 44 b decodes the communicationsignal in the line into a digital signal which is fed to receiver 46 foranalyzing the data-link and higher OSI layers. The digital signal isthen fed to a line driver 44 a which encodes the communication signalagain. The pair consisting of line receiver 44 b and line driver 44 athus form a communication signal repeater which performs a transparentrouting of the communication signal from ‘left’ to ‘right’. The delaybetween input and output is negligible, in the order of nano-seconds ormicro-seconds.

Similarly, FIG. 5 b allows for a routing from ‘right’ to ‘left’. Thedirection of repeater/router 44 is controlled by control, logic, andprocessing unit 47, via control lines (omitted for clarity from FIG. 5).

Whereas FIGS. 5 a and 5 b describe a node which does not generate anydata (but only receives and transfers the data in the network), FIGS. 5c and 5 d illustrate nodes in the transmitting state. In both cases, thenode transmits data to both the right and left connections via therespective line coupler. In FIG. 5 c, two line drivers 44 a are used,one for each direction. In FIG. 5 d, a single line driver 44 a is used,driving both directions from a single unit. Both embodiments can be usedinterchangeably. In most cases, the line driver and line couplercharacteristics will be the basis for selecting one configuration inpreference over the other. For example, if the line driver is capable ofdriving a single line only, the configuration of FIG. 5 c should beused.

FIG. 6 shows a network 60 according to the present invention.Electrically-conducting communication media of lines 61 a, 61 b, 61 c,and 61 d are used to interconnect the nodes. At least two conductors areused in the communication media. For example, coaxial cables or coppertwisted-pairs may be used. For clarity only, the figures hereinillustrate the use of a single twisted-pair in non-limiting examples.

Nodes 62, 63, 64, 65 and 66 are all the based on node 40 as describedpreviously. Nodes 62, 65, and 66 are in ‘Right’to ‘Left’state asillustrated in FIG. 5 b, whereas node 64 is in ‘Left’to ‘Right’state asillustrated in FIG. 5 a. Node 63 is the data generating node as in FIG.5 c and 5 d. The network in FIG. 6 shows one possible state of thenetwork, wherein node 63 is the data-generating node, while all othernodes serve as receivers and repeaters, receiving the data andre-transmitting the data to the next sequential node. In order tosupport dynamic reconfiguration, nodes can simultaneously have more thanone operational mode. In a non-limiting fashion a node can have:

-   -   a data-generating operational mode, wherein a node functions as        a source of data, and transmits this data to other nodes;    -   a receiving operational mode, wherein the node receives data        from another node; and    -   a repeating operational mode, wherein the node functions as a        repeater of data received from one given node by re-transmitting        this data to another given node.

While the network is functioning, the current operational mode of a nodeis selectable from the available operational modes. Some operationalmodes may be mutually exclusive, while others may be selectedsimultaneously. For example, the data-generating operational mode isexclusive of the repeating operational mode, whereas the receivingoperational mode may be selected at the same time as the repeatingoperational mode.

In most applications, more than one node can serve as a data-generatingnode at different times. In such a case, the network states will bechanged as a function of time according to predetermined logic andcontrol, in order to allow each data generating node an opportunity totransmit. However, no more than a single node can serve asdata-generating node at a time. While a node is serving asdata-generating node, all other nodes states are accordingly set to berepeaters and/or receivers, to allow for data distribution along thenetwork. Nodes located ‘left’ of the data generating node will be in a‘right to left’ state, while nodes located ‘right’ of thedata-generating node will be in a ‘left to right’ state.

It should be clear that, whereas the nodes at the network ends, the‘left-most’ node 62 and the ‘right-most’ node 64 could use the samestructure as shown in FIG. 4 (and can be implemented in the same way asall other nodes in the network), the end nodes utilize only single lineconnection. Thus these end nodes can be implemented using a single linecoupler and single line driver.

It should also be clear that one or more of the nodes in the networkneed not be connected to a payload, as is illustrated for node 65 inFIG. 6 This may be the case where the attenuation in the line is toohigh (e.g. a line is too long), and a node serves mainly as a repeater.In such a case, payload interface 48 would not be required.

Network Powering.

FIG. 6 illustrates a network wherein each node is locally powered by alocal power source 52, which supplies electrical power for operating thecomponents of the network. Alternatively, the network communicationmedia can be used for power distribution. In one embodiment of thepresent invention, the power is distributed via dedicated lines, such asby the use of two additional wires within the same cable. In a preferredembodiment, the same wires can be used for both data communication andpower distribution. The latter configuration is described in co-pendingU.S. patent application Ser. No. 09/141,321, filed by the presentinventor on Aug. 27, 1998, which is applicable to the network discussedherein and incorporated by reference. FIG. 8 illustrates such a network,allowing for single power-supply to be used for powering the wholenetwork.

When the same wires are used for both communication and power, the node40 should be modified to include a power/data combiner/splitter 71 asshown in FIG. 7 A node 70 is shown with two power/datacombiner/splitters 71 coupled to line couplers 42 and 43. A node such asnode 70 can receive power from either the left or the right sides orfrom both sides, and carry the power to the non-powered side. Beingpowered from the network, no power source interface will be usuallysupported for such a configuration. The power source feeding the networkcan connect thereto via dedicated couplers or via one or more of thenodes, modified to support such capability.

Circular Topology.

While the foregoing description applies the present invention to alinear topology, the present invention can also be implemented using acircular topology for ‘ring’ type networks. In one embodiment, both endsof the network are connected to a node which is configured to receivefrom both sides, hence including two receivers. However, FIG. 8 shows apreferred embodiment of a network 80. In network 80, all nodes exceptthe data-generating node are configured to the transparent repeaterstate, either uniformly ‘right-to-left’ or uniformly ‘left-to-right’. Anode 90 in the data-generating state is modified as illustrated in FIGS.9 a and 9 b. Node 90 can transmit to one side and receive from theother. In FIG. 9 a node 90 can transmit to the left side and receivefrom the right side. Similarly, in FIG. 9 b node 90 can transmit to theright side and receive from the left side. Either state can be used incircular topology. In FIG. 8, node 90 is in the state shown in FIG. 9 a.Alternatively, node 90 can be in the state shown in FIG. 9 b. All othernodes of FIG. 8 are configured in the ‘right-to-left’ direction. In bothcases, the data-generating node 90 transmits to one side and receivesfrom the other. The receiving functionality of node 90 can be used formonitoring the network, to insure that the data path is available and iserror-free. However, this receiver functionality is an option only, anddoes not have to be implemented.

For compactness, FIG. 8 demonstrates both the power feeding via thenetwork and the circular topology together, but these features areindependent and may be implemented separately.

Network Control.

As described above, the operation of the network (either bus or circulartopology) switches from state to state. Each state is characterized byhaving a specific node functioning as data-generating node at a time,while all other nodes serve as repeaters and receivers, routing the datacoming from the data-generating node. Hence, there is a need for anetwork controller to determine which node in the network will be thedata-generating node.

Various techniques can be used to implement such a network controller.The network controller can select nodes sequentially, by means of tokenpassing from node to node (similar to that of the Token-Ring network).The network controller can be external to the network, using dedicatedcommunication media. Preferably, the network controller will be embeddedand will manage the network states via signals transported by thenetwork itself. In most cases, each node should be allocated an address,enabling data routing in the network from arbitrary node to arbitrarynode.

Another popular method of network discipline is ‘master/slave’operation. In another embodiment of the present invention, one of thenodes will be designated as the master node. In the initial state, thisnode serves as the data-generating node, and while in this state directsother nodes to transmit. During the following state the selected nodewill serve as the data-generating node. This two-state sequence will berepeated, with a different node selected to be the data-generating nodein each subsequent cycle, according to predetermined logic or underexternal control.

Dual Discipline Network.

The network taught by U.S. Pat. No. 5,841,360 to the present inventor,herein referred to as the “PSIC Network”, employs multiple communicationlinks, independent of each other. Such a network supports severalfeatures which are not available in the previously-described network,such as automatic addressing, fault localization, and circular topologyredundancy in the case of single failure.

In order to exploit the benefits of both these network types it ispossible to construct a network which supports both disciplines. and canbe controlled to be either in one discipline or in the other. Forexample, the network may start as PSIC Network. During this start-upperiod, automatic addressing and fault localization will be performed.Thereafter, the network may configure itself to work according to thisapplication or may use time-sharing and alternately switch between bothconfigurations.

FIG. 10 shows a schematic view of a node 100 which is capable of bothroles. The state of node 100 is determined by switches 101, 104, 102,and 103, designated SW1, SW2, SW3 and SW4 respectively. These switchesare controlled by control, logic, and processing unit 47. Node 100employs transmitters 45 a and 45 b, as well as receivers 46 a and 46 b.Line driver 44 a serves the right port; while line driver 44 a 1 servesthe left connection. Similarly, line receivers 44 b and 44 b 1 areconnected to the right and left interfaces respectively.

FIG. 12 lists the various possible node states for node 100 (FIG. 10).The states in FIG. 12 are given in a Node State column, and the switchsettings are given in SW1, SW2, SW3, and SW4 columns. In a‘Right-to-left’ state, data received in the right port is handled byline receiver 44 b and fed to line receiver 46 b. Simultaneously, thereceived data is fed to line driver 44 a 1, which transmits to the leftside. Thus, the functionality shown in FIG. 5 b is obtained. In asimilar way, the ‘Left-to-right’ state is implemented to achieve afunctionality as shown in FIG. 5 a. In the latter case, line receiver 46a is the active one.

In the ‘transmit both sides’ state, transmitter 45 a transmits to bothports using line drivers 44 a and 44 a 1, implementing the functionalityshown in FIG. 5 c. In the ‘receive both sides’ state, each receiver isconnected to single line coupler, and no line driver is activated. Thisis expected to be the state when the network is idle or as an interimstate while switching between states, in order to avoid data collisionscaused by two or more transmitters active over the same link.

The ‘transmit right receive left’ state reflects the state shown in FIG.9 b. Similarly, the ‘transmit left receive right’ state reflects thefunctionality shown in FIG. 9 a.

In the ‘transmit/receive both sides’ state, the node can receive andtransmit in both interfaces simultaneously, thus implementing the fullPSIC Network functionality.

Nodes with More than Two Line Connections

Whereas the foregoing discussion describes a node having two linecouplers (which may be reduced to single interface in the case of anend-unit in a network employing ‘bus’ topology), it is obvious thatthree or more such interfaces could also be used. In such a case, atleast one additional repeater/router must be added for each additionalinterface. For example, FIG. 11 illustrates a node 110 having threeinterfaces, where an additional interface is designated as ‘up’, anduses a line coupler 112 for interfacing to a line 111. In order tosupport the interconnection between all three ports, threerepeater/router units 44 are used, each constructed as describedpreviously and suitable for connecting two ports. In some applications,where the connectivity requirements can be reduced, any two out of thethree ports may be used.

Similarly, additional interfaces can be used. Furthermore, a network canemploy nodes of different interface capacities, which can be freelyconnected to construct a network of arbitrary topology. In all cases,the basic rule that each communication link connect only two nodes mustbe observed. Furthermore, the network logic embedded in the nodes has toinsure that no more than a single node generates data, while all othersmust be in the transparent repeater/router state, directed from thedata-generating node.

Implementation.

Implementing any of the above schemes is straightforward for anyoneskilled in the art. In one embodiment, RS-485 (EIA-485) is employed forthe physical layer. In such a case, line driver 44 a and line receiver44 b are directly implemented using a common RS-485 line driver or linereceiver, respectively. Similarly, the switches illustrated in FIG. 10can be implemented using manually-activated switches, relays, analogswitches. or digital switches/multi-plexers. Except in the case ofmanual switches, switching is controlled electronically.

Repeaters and regenerators are known in both prior-art WAN (Wide AreaNetwork) and LAN (Local area network) systems, mainly for the purpose ofallowing operation over lengthy connections. However, there are majordifferences between those networks and the present invention. First,most prior-art repeaters employ single input and single output. Thepresent invention allows for multiple ports. Second, prior-art repeatersare unidirectional, while the present invention is not restricted to aspecific direction of data flow. Additionally, the present inventionrequires a control mechanism (a network controller) for determining thedata flow direction, whereas prior-art systems, being unidirectional, donot require such control. In most prior-art networks, units in thenetwork can be clearly defined as either payload-associated units ordedicated repeaters. Such a distinction is not valid when implementing anetwork according to the present invention, since eachpayload-associated unit in the network also includes the repeaterfunctionality.

Although a network according to the present invention, when configuredin circular topology, can be superficially similar to a Token-Ringnetwork, there are major differences between them. In a Token-Ringnetwork, there is a single constant direction of data flow. The presentinvention does not impose single direction of data flow, but the flowmay change as part of the network operation. In addition, in Token-Ringnetworks the data-generating unit is sequentially allocated according tothe network topology. In the present invention, the data-generating nodeneed not be chosen according to any specific rule, although sequentialselection of the data-generating node is possible.

While the invention has been described with respect to a limited numberof embodiments, it will be appreciated that many variations,modifications and other applications of the invention may be made.

What is claimed is:
 1. A control network in a building for wiredcoupling of at least one analog device to a data unit, the networkcomprising: a plurality of nodes including first, second and thirdnodes; and a plurality of wiring segments including first and secondwiring segments, each wiring segment comprising at least two conductors,wherein said first wiring segment connects said first and second nodestogether in a point-to-point connection, and said second wiring segmentconnects said second and third nodes together in a point-to-pointconnection, wherein: said first and second nodes effect bi-directionalcommunication of serial digital data over said first wiring segment andsaid second and third nodes effect bi-directional communication ofserial digital data over said second wiring segment, at least one ofsaid nodes is connectable to a data unit for coupling the serial digitaldata carried over at least one of said wiring segments to the data unit,at least one of said nodes comprises an analog/digital or digital/analogconverter connectable to the analog device for coupling the serialdigital data carried over said at least one of said wiring segments tothe analog device, the analog device is a sensor or an actuator, each ofsaid nodes is addressable in said network, and each of said nodes isconnected by a respective pair of said wiring segments to only two othernodes, said nodes are connected by the wiring segments in a ringconfiguration, each of said nodes is in direct signal conductingcommunication only with a unique pair of other nodes and one of the dataunit and the analog device, and each of said nodes is operative to be ina selected state to conduct data in both directions around the ring. 2.The network according to claim 1, wherein at least one of said wiringsegments comprises a twisted wire pair or a coaxial cable.
 3. Thenetwork according to claim 1, wherein the serial digital data ispacket-based.
 4. The network according to claim 1, wherein at least oneof said wiring segments concurrently carries a direct current (DC) powersignal, and at least one of said nodes is at least in part powered bythe power signal.
 5. The network according to claim 1, wherein at leastone of said nodes is connectable to a direct current (DC) power sourcesupplying a DC power signal, and at least one of said wiring segmentsconcurrently carries the power signal.
 6. The network according to claim1, wherein said nodes are operative to reroute serial digital data inthe event of failure of one of said wiring segments.
 7. The networkaccording to claim 1, wherein each of said nodes has a manually assignedaddress.
 8. The network according to claim 1, wherein each of said nodeshas an automatically assigned address.
 9. The network according to claim1, wherein each of said nodes has an address assigned by a data unitconnected to said node.
 10. The network according to claim 1, wherein atleast one of said nodes is operative to power a device connectedthereto.
 11. The network according to claim 1, wherein at least one ofsaid nodes is operative to power the analog device.
 12. The networkaccording to claim 1, wherein the at least one analog device includes afirst analog device in the form of a sensor to which a first one of saidnodes is connectable and a second analog device in the form of anactuator to a which a second one of said nodes is connectable, andwherein operation of the actuator is dependent upon the sensor output.13. The network according to claim 1, wherein the at least one analogdevice is an analog sensor, to which one of said nodes is connectable,for measuring a physical phenomenon, and said one of said nodes furthercomprises an analog to digital converter for converting analog signalsfrom the analog sensor into serial digital data.
 14. The networkaccording to claim 1, wherein the at least one analog device is ananalog actuator, to which one of said nodes is connectable, forproducing a physical phenomenon, and said one of said nodes furthercomprises a digital to analog converter for converting serial digitaldata into analog signals for the analog actuator.
 15. The networkaccording to claim 1, wherein at least one of said nodes is operative torepeat at least part of the serial digital data received from one wiringsegment connected to said at least one node to the other wiring segmentconnected to said at least one node.
 16. The network according to claim1, wherein all the communication links are operative to communicate inhalf duplex mode.
 17. The network according to claim 1, wherein all thecommunication links are operative to communicate in full duplex mode.18. The network according to claim 1, wherein at least one of the wiringsegments is operative to carry a video or voice signal.
 19. A local areanetwork comprising: a plurality of nodes including a first nodeincluding a first data port for coupling to a first component, a secondnode including a second data port for coupling to a second component anda third node including a third data port for coupling to a thirdcomponent; a plurality of wiring segments each having two ends andconsisting of only two conductors, said plurality of wiring segmentsincluding a first wiring segment connecting only said first and secondnodes in a point-to-point connection for a first half-duplex datacommunication of serial digital data over said first wiring segmentbetween said first and second nodes, and a second wiring segmentconnecting only said first and third nodes in a point-to-pointconnection for a second half-duplex data communication of serial digitaldata over said second wiring segment between said first and third nodes,wherein: each of said nodes is connected by a respective pair of saidwiring segments to only two other nodes, said nodes are connected by thewiring segments in a ring configuration, and each of said nodes is indirect signal conducting communication with a unique pair of other nodesand one component; and said network is operative to be in at least aselected one of first and second states; in the first state, saidnetwork is operative to conduct data from said second data port oversaid first wiring segment from said second node to said first node,repeat the data at said first node to said second wiring segment, andconduct the repeated data over said second wiring segment from saidfirst node to said third node; and in the second state, said network isoperative to conduct data from said third data port over said secondwiring segment from said third node to said first node, repeat the dataat said first node to said first wiring segment, and conduct therepeated data over said first wiring segment from said first node tosaid second node.
 20. The network according to claim 19, wherein atleast one of said nodes further comprises a control, logic andprocessing unit connected in said at least one node for controlling saidat least one node to establish a selected one of said first and secondstates.
 21. The network according to claim 20, wherein each of saidnodes is housed in a single enclosure.
 22. The network according toclaim 19, wherein said network periodically sequentially shifts betweenthe first and second states.
 23. The network according to claim 19wherein each of said nodes is addressable in said network.
 24. Thenetwork according to claim 19, wherein said network is further operativeto reroute digital data in the event of failure of one of said wiringsegments.
 25. The network according to claim 19 further comprising athird wiring segment having two ends and consisting of only twoconductors, said third wiring segment being connected to said firstnode, and wherein in the first state, said first node is operative torepeat data from said first wiring segment to the third wiring segment,and in said second state said first node is operative to repeat datafrom said second wiring segment to said third wiring segment.
 26. Thenetwork according to claim 19, wherein at least one of said wiringsegments concurrently carries a power signal over said two conductorssubstantially without interfering with data communication over said atleast one wiring segment, and at least part of at least one of saidnodes is powered from the power signal.
 27. The network according toclaim 19, wherein at least one of said wiring segments concurrentlycarries a power signal over the two conductors substantially withoutinterfering with the data communication, and at least one component ispowered from the power signal carried over a wiring segment connected tothe respective node.
 28. The network according to claim 19, wherein saidtwo conductors of at least one of said wiring segments concurrentlycarry a power signal over substantially without interfering with thedata communication, and at least one of said nodes is connectable to apower source for coupling the power signal to the power source.
 29. Thenetwork according to claim 19, wherein at least one out of said firstand second wiring segments is one of a twisted wire pair or a coaxialcable.
 30. The network according to claim 19, wherein said network isfurther operative for analog sensing and control, wherein said networkfurther comprises an analog port and a converter for converting betweenanalog and digital signals coupled between said analog port and saidport of one of said nodes, and said analog port is couplable to ananalog sensor or to an analog actuator constituting one of thecomponents.
 31. The network according to claim 30, wherein said networkis further operative to carry video or voice signals.
 32. The networkaccording to claim 19 wherein at least one of said nodes is enclosed ina single enclosure together within a respective connected component. 33.The network according to claim 19, wherein said network is furtheroperative to be in a third state in which data received from the firstcomponent via said first data port is repeated to both said first andsecond wiring segments.
 34. A local area network for carrying power anddigital data, said network comprising: a plurality of nodes including afirst node including a first data port for coupling to a first dataunit, a second node including a second data port for coupling to asecond data unit and a third node including a third data port forcoupling to a third data unit; a plurality of wiring segments eachhaving two ends and comprising a first coaxial cable or at least onefirst twisted wire pair, wherein each end of each of said wiringsegments is terminated in a connector, said plurality of wiring segmentsincluding first and second wiring segments, said first wiring segmentconnecting only said first and second nodes in a point-to-pointconnection for a first full-duplex data communication of serial digitaldata over said first wiring segment between the first and second dataunits, and said first wiring segment being connected to concurrentlycarry a first power signal substantially without interfering with thefirst communication of serial digital data and said second wiringsegment connecting only said first and third nodes in a point-to-pointconnection for a second full-duplex communication of serial digital dataover said second wiring segment between the first and third data units,and said second wiring segment being connected to concurrently carry asecond power signal substantially without interfering with the secondcommunication of serial digital data, wherein: each of said nodes isconnected by a respective pair of said wiring segments to only two othernodes, said nodes are connected by the wiring segments in a ringconfiguration, and each of said nodes is in direct signal conductingcommunication with a unique pair of other nodes, said first node isconnectable to a power supply to be powered from the power supply, andthe first and second power signals are provided by the power supply,said second node is at least in part powered by the first power signal,said third node is at least in part powered by the second power signal,and each of said nodes is addressable in said network.
 35. The networkaccording to claim 34, wherein: said network is further operative to bein a selected one of at least first and second states; in the firststate, data received from said second data port is carried over saidfirst wiring segment from said second node to said first node, repeatedby the first node to said second wiring segment, and carried over saidsecond wiring segment from said first node to said third node; and inthe second state, data received from said third data port is carriedover said second wiring segment from said third node to said first node,repeated by said first node to said first wiring segment, and carriedover said first wiring segment from said first node to said second node.36. The network according to claim 34, wherein said network is furtheroperative to reroute digital data in the event of failure of one of saidwiring segments.
 37. The network according to claim 34, wherein saidnetwork is further operative for analog sensing and control, whereinsaid network further comprises an analog port and a converter forconverting between analog and digital signals coupled between saidanalog port and said data port of one of the nodes, and said analog portis couplable to an analog sensor or to an analog actuator.
 38. Thenetwork according to claim 37, wherein said network is further operativeto carry video or voice signals.
 39. The network according to claim 34,further comprising a single enclosure housing at least one of said nodestogether with a respective connected data unit.
 40. The networkaccording to claim 34, wherein said network is further operative to bein a third state in which data received from the first data unit viasaid first data port is repeated to both said first and second wiringsegments.
 41. The network according to claim 34 wherein at least one ofthe connected data units is at least in part powered by a power signalcarried over one of said wiring segments.
 42. The network according toclaim 34, wherein at least one of said wiring segments comprisesdedicated power conductors carrying only a respective power signal anddata conductors carrying distinct from the power conductors and carryingrespective serial digital data.
 43. The network according to claim 34,wherein at least one of said wiring segments carries a respective powersignal and data over the same conductors.
 44. The network according toclaim 34 wherein at least one of said nodes is housed together with aconnected data unit.